Academic Commons Search Resultshttp://academiccommons.columbia.edu/catalog.rss?f%5Bsubject_facet%5D%5B%5D=Biomechanics&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usThe Effects of Arrhythmogenic Right Ventricular Cardiomyopathy-Causing Proteins on the Mechanical and Signaling Properties of Cardiac Myocyteshttp://academiccommons.columbia.edu/catalog/ac:178173
Hariharan, Venkateshhttp://dx.doi.org/10.7916/D84M933GTue, 30 Sep 2014 00:00:00 +0000Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by a high incidence of lethal ventricular arrhythmias, fibrofatty replacement of myocardium, and can account for up to 20% of sudden cardiac death (SCD) cases in the young. Typically involving autosomal dominant transmission, germline mutations in genes encoding desmosomal proteins have been identified as a cause of ARVC, although the pathogenesis of the disease is still unclear. While early detection and treatment can provide a normal life expectancy for the majority of patients, with less than 10% progressing to overt right ventricular failure, low genetic penetrance and epigenetic modifiers (such as endurance exercise) can make the condition difficult to diagnose. Addressing this clinical challenge requires a better understanding of the defective molecular mechanisms that underlie the disease. To that end, the goal of this dissertation is to provide insight into the effects of ARVC-causing mutant proteins on the mechanical and signaling properties of cardiac myocytes. Using elastography and histological techniques, we begin by characterizing the structural and mechanical properties of the native right ventricular myocardium, particularly the right ventricular apex (RVA). Because the RVA is a key site for development of arrhythmias and a potential pacing target, a careful characterization of its structure and mechanical properties are essential for understanding its role in cardiac physiology. In the first section of this dissertation, we perform a systematic analysis of the structural features and mechanical strains in the heart, focusing on the RVA region. More than half of ARVC patients exhibit one or more mutations in genes encoding desmosomal proteins. This has led many investigators to suggest that ARVC is a "disease of the desmosome" in which defective cell-cell adhesion plays a critical pathogenic role, although direct evidence for this hypothesis is lacking. To gain greater insights into potential mechanisms by which desmosomal mutations cause ARVC, we next characterize biomechanical properties and responses to shear stress (motivated by our results in the previous section) in neonatal rat ventricular myocytes expressing two distinct mutant forms of the desmosomal protein plakoglobin which have been linked to ARVC in patients. We show that ARVC-causing mutations in plakoglobin lead to altered cellular distribution of plakoglobin, without alterations in cell mechanical properties or certain early signaling pathways. The identification of defective molecular mechanisms that are common across ARVC-patients remains a strategic area of research. Specifically, recent studies have investigated the mechanistic basis for different ARVC-causing mutations in hopes of identifying common defects in a signaling pathway - information that could be used to develop diagnostic tests or identify therapeutic targets. In the last section of this dissertation, we investigate the effects of mutant plakophilin-2 expression, and repeat key experiments performed in the previous section to identify common defects in mechanical and signaling properties. We identify a common, underlying defect in ARVC pathogenesis. Specifically, we show that disease-causing mutations across different desmosomal proteins can cause the cell to respond abnormally to mechanical shear stress with respect to plakoglobin trafficking.Biomedical engineering, Biomechanicsvh2198Biomedical EngineeringDissertationsFast dynamics of supercoiled DNA revealed by single-molecule experiments.http://academiccommons.columbia.edu/catalog/ac:177522
Crut, Aurelien; Koster, Daniel A.; Seidel, Ralf; Wiggins, Chris H.; Dekker, Nynke H.http://dx.doi.org/10.7916/D8S75DW3Sat, 20 Sep 2014 00:00:00 +0000The dynamics of supercoiled DNA play an important role in various cellular processes such as transcription and replication that involve DNA supercoiling. We present experiments that enhance our understanding of these dynamics by measuring the intrinsic response of single DNA molecules to sudden changes in tension or torsion. The observed dynamics can be accurately described by quasistatic models, independent of the degree of supercoiling initially present in the molecules. In particular, the dynamics are not affected by the continuous removal of the plectonemes. These results set an upper bound on the hydrodynamic drag opposing plectoneme removal, and thus provide a quantitative baseline for the dynamics of bare DNA.Biophysics, Biomechanicschw2Applied Physics and Applied MathematicsArticlesModeling Air-flow in the Tracheobronchial Tree using Computational Fluid Dynamicshttp://academiccommons.columbia.edu/catalog/ac:177139
Kaya, Ilhan; Santhanam, Anand P.; Imielinska, Celina Z.; Rolland, Jannickhttp://dx.doi.org/10.7916/D80C4T99Thu, 11 Sep 2014 00:00:00 +0000In this paper, we present a biomechanical framework to model air-flow inside the bronchus and deformations across the tracheobronchial tree, pipeline for the simulator, theory and initial steps to realize this framework on a highly parallel graphical processing unit (GPU). We discuss the main challenges expected and encountered to date. By using computational fluid dynamics (CFD) and computational solid dynamics (CSD) principles, we propose a numerical simulation framework that includes a biomechanical model of the tracheobronchial tree to simulate air flow inside the tree, on GPU in real-time. The proposed 3D biomechanical model to simulate the air inside the lungs coupled with a deformation model of the tracheobronchial tree, expressed through fluid-structure interaction, can be used to predict the transformations of the voxels from a 4D computed tomography (4DCT) dataset. Additionally, the proposed multi-functional CFD and CSD based framework is suitable for clinical applications such as adaptive lung radiotherapy, and a regional alveolar ventilation estimation.Biomedical engineering, Bioinformatics, Biomechanicsci42Biomedical InformaticsConferencesMerging Augmented Reality and Anatomically Correct 3D Models in the Development of a Training Tool for Endotracheal Intubationhttp://academiccommons.columbia.edu/catalog/ac:177145
Rolland, Jannick; Davis, Larry; Hamza-Lup, Felix G.; Norfleet, Jack; Imielinska, Celina Z.; Kerner, Karen F.http://dx.doi.org/10.7916/D8QV3K1SThu, 11 Sep 2014 00:00:00 +0000Augmented reality is often used for medical training systems in which the user visualizes 3D information superimposed on the real world. In this context, we introduce a augmented reality tool to train the medical practitioner hand-eye coordination in performing critical procedures such as endotracheal intbation.Biomedical engineering, Bioinformatics, Biomechanicsci42, kfk9Biomedical Informatics, Computer Science, MedicineConferencesCell Mechanics Regulate Mesenchymal Stem Cell Morphology and T Cell Activationhttp://academiccommons.columbia.edu/catalog/ac:175418
Santos, Luishttp://dx.doi.org/10.7916/D8K64G7TMon, 07 Jul 2014 00:00:00 +0000The work of my thesis is the cumulative result of 6 years of research in Prof. Michael P. Sheetz laboratory at the Biological Sciences Department of Columbia University, within the collaborative framework of the Nanotechnology Center for Mechanobiology, an interdisciplinary and multi-institutional center for the study of cell mechanics, involving, among other institutions, the Applied Physics department at Columbia University, and the Schools of Medicine of University of Pennsylvania, New York University, and Mt Sinai. In Chapter 1, I provide an overview of the field of mechanobiology, with an emphasis on the implications of cell-extracellular matrix and cell-cell attachment on cell function. In Chapter 2, I present the aims of the thesis, with a focus on the two cell systems used in the projects described: human mesenchymal stem cells, and T cells. Then, Chapters 3-5 represent the main body of my thesis, where I present detailed descriptions of the projects that I worked on and that successfully made it into scientific publications or that are in preparation for publication. In Chapter 3, I analyze how matrix chemistry and substrate rigidity affect human mesenchymal stem cell morphology in the context of lineage differentiation, and speculate on potential mechanisms that cells use to sense local rigidity. In Chapter 4, I present a new substrate design that facilitates live visualization of the interface formed between a T cell and an antigen presenting cell, i.e. the immunological synapse, and discuss the impact of intercellular forces on T cell activation. In Chapter 5, I explore the molecular mechanism of Cas-L mechanical activation at the immunological synapse of T cells, and demonstrate how Cas-L regulates T cell activation in the context of an immune response. Finally, in Chapter 6, I lay down the main conclusions of the thesis, and discuss ongoing projects that directly follow up on the results of this thesis.Biomechanics, Cellular biology, Immunologylcs2119Biological SciencesDissertationsBiomechanical Assessment and Monitoring of Thermal Ablation Using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)http://academiccommons.columbia.edu/catalog/ac:168502
Hou, Yihttp://dx.doi.org/10.7916/D8FJ2DR5Mon, 06 Jan 2014 00:00:00 +0000Cancer remains, one of the major public health problems in the United States as well as many other countries worldwide. According to According to the World Health Organization, cancer is currently the leading cause of death worldwide, accounting for 7.6 million deaths annually, and 25% of the annual death was due to Cancer during the year of 2011. In the long history of the cancer treatment field, many treatment options have been established up to date. Traditional procedures include surgical procedures as well as systemic therapies such as biologic therapy, chemotherapy, hormone therapy, and radiation therapy. Nevertheless, side-effects are often associated with such procedures due to the systemic delivery across the entire body. Recently technologies have been focused on localized therapy under minimally or noninvasive procedure with imaging-guidance, such as cryoablation, laser ablation, radio‐frequency (RF) ablation, and High Intensity F-ocused Ultrasound (HIFU). HIFU is a non-invasive procedure aims to coagulate tissue thermally at a localized focal zone created with noninvasively emitting a set of focused ultrasound beams while the surrounding healthy tissues remain relatively untreated. Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a dynamic, radiation-force-based imaging technique, which utilizes a single HIFU transducer by emitting an Amplitude-modulated (AM) beam to both thermally ablate the tumor while inducing a stable oscillatory tissue displacement at its focal zone. The oscillatory response is then estimated by a cross-correlation based motion tracking technique on the signal collected by a confocally-aligned diagnostic transducer. HMIFU addresses the most critical aspect and one of the major unmet needs of HIFU treatment, which is the ability to perform real-time monitoring and mapping of tissue property change during the HIFU treatment. In this dissertation, both the assessment and monitoring aspects of HMIFU have been investigated fundamentally and experimentally through development of both a 1-D and 2-D based system. The performance assessment of HMIFU technique in depicting the lesion size increase as well as the lesion-to-background displacement contrast was first demonstrated using a 3D, FE-based interdisciplinary simulation framework. Through the development of 1-D HMIFU system, a multi-parametric monitoring approach was presented where presented where the focal HMI displacement, phase shift (Δφ), and correlation coefficients were monitored along with thermocouple and PCD under the HIFU treatment sequence with boiling and slow denaturation. For HIFU treatments with slow denaturation, consistent displacement increase-then-decrease trend was observed, indicating tissue softening-then-stiffening and phase shift increased with treatment time in agreement with mechanical testing outcomes. The correlation coefficient remained high throughout the entire treatment time under a minimized broadband energy and boiling mechanism. Contrarily, both displacement and phase shift changes lacked consistency under HIFU treatment sequences with boiling due to the presence of strong boiling mechanism confirmed by both PCD and thermocouple monitoring. In order to facilitate its clinical translation, a fully-integrated, clinically 2D real-time HMIFU system was also developed, which is capable of providing 2D real-time streaming during HIFU treatment up to 15 Hz without interruption. Reproducibility studies of the system showed consistent displacement estimation on tissue-mimicking phantoms as well as monitoring of tissue-softening-then-stiffening phase change across 16 out of 19 liver specimens (Increasing rate in phase shift (Δφ): 0.73±0.69 %/s, Decreasing rate in phase shift (Δφ): 0.60±0.19 %/s) along with thermocouple monitoring (Increasing: 0.84±1.15 %/ °C, Decreasing: 2.03± 0.93%/ °C) and validation of tissue stiffening using mechanical testing. In addition, the 2-D HMIFU system feasibility on preclinical pancreatic tumor mice model was also demonstrated in vivo, where HMI displacement decreases were observed across three of five treatment locations on the kP(f)c model at 20.8±6.84, 18.6±1.46, and 24.0±5.43%, as well as across four of the seven treatment locations on the KPC model at 39.5±2.98%, 34.5±21.5%, 16.0±3.05%, and 35.0±3.12% along with H and E histological confirmation. In order to improve the quantitative monitoring aspect of HMIFU, a novel, model-independent method for the estimating Young's modulus based on strain profile was also implemented, where 1-D HMIFU system showed feasibilities on polyacrylamide phantom (EHMI/E ≈ 2.3) and liver specimen (EHMI/E ≈ 8.1), and 2-D HMIFU system showed feasibilities on copolymer phantom(EHMI/E ≈ 30.4), liver specimen(EHMI/E ≈ 211.3), as well as HIFU treated liver specimen(EHMI,end/EHMI,beginning ≈ 5.96). In conclusion, the outcomes from the aforementioned studies successfully showed the feasibility of both HMIFU systems in multi-parametric monitoring of HIFU treatment with slow denaturation and boiling, which prepares its stage towards clinical translation.Biomedical engineering, Biomechanics, Acousticsyh2367Biomedical EngineeringDissertationsAugmenting and Exploiting Auditory Perception for Complex Scene Analysishttp://academiccommons.columbia.edu/catalog/ac:159307
Ellis, Daniel P. W.http://hdl.handle.net/10022/AC:P:19783Thu, 18 Apr 2013 00:00:00 +0000I was invited to participate in this workshop that advises DARPA on scientific frontiers; the topic was ways to use technology to enhance individual senses. My talk covers some basics of auditory/acoustic scene analysis in humans and machines, and speculates about future "super sense" augmentations.Audiology, Biomechanicsde171Electrical EngineeringPresentationsApplication of a Novel Quasi-3D Microscopy Technique to Investigate Early Osteocyte Mechanotransduction Eventshttp://academiccommons.columbia.edu/catalog/ac:155913
Baik, Andrewhttp://hdl.handle.net/10022/AC:P:18830Fri, 25 Jan 2013 00:00:00 +0000The objective of this thesis is to observe and characterize the early mechanical and biochemical events in osteocyte mechanotransduction. Physical forces have been increasingly implicated in normal physiological and pathological cellular activities of osteocytes. The mechanotransduction process in osteocytes involves spatiotemporally complex changes in cytoskeletal organization, signal activation, and whole cell mechanical properties. Most in vitro biophysical techniques currently available sacrifice either spatial or temporal resolution and are unable to visualize 3D cellular behavior on the millisecond time scale. Here, we develop a novel multi-channel quasi-3D microscopy technique to simultaneously visualize and measure whole-cell mechanics, intracellular cytoskeletal deformation, and biochemical signal activation under fluid shear flow. The technique was applied to visualize cell dilatation and cytoskeletal deformation in osteocytes under steady fluid shear flow. Analysis of the plasma membrane and either the intracellular actin or microtubule cytoskeletal networks provided characterization of their deformations over time. No volumetric dilatation of the whole cell was observed under flow, and both cytoskeletal networks experienced primarily tensile viscoelastic creep and recovery in all measured strain components. Intra- and inter- cellular mechanical heterogeneity was observed in both cytoskeletal networks. Cytoskeletal disruption pointed towards a unidirectional mechanical interaction where microtubule networks affected actin network strains, but not vice versa. The second study in this thesis investigated the effects of steady and oscillatory flow on the actin and microtubule networks within the same cell. Shear strain was the predominant strain in both steady and oscillatory flows, in the form of viscoelastic creep and elastic oscillations, respectively. Under oscillatory fluid shear flow, the actin networks displayed an oscillatory strain profile more often than the MT networks in all the strains tested and had a higher peak-to-trough magnitude. Taken together with the first study, the actin networks were determined to be the more responsive cytoskeletal networks in osteocytes to fluid flow and may play a bigger role in mechanotransduction. The final culminating study tracked [Ca+2]i and F-actin network strains simultaneously in a single osteocyte. We demonstrated novel osteocyte mechano- and transduction behavior where [Ca+2]i oscillations activate phasic actomyosin contractions using a smooth muscle-like mechanism. Fluid shear, ATP, and ionomycin induced [Ca+2]i signaling with a subsequent compression and recovery in actin strains of the cell, being most apparent in the height direction strain. This contraction was reversible over the period of hundreds of seconds. ML-7, a myosin light chain kinase inhibitor, significantly slowed down the kinetics of contraction initiation, but blebbistatin, a potent skeletal and non-muscle inhibitor, had no effect on the actin contraction. Furthermore, smooth muscle contraction-related proteins were detected by Western blot. The observation of muscle-like contractility in osteocytes demonstrates a possible positive feedback mechanism of osteocytes to activate mechanotransduction pathways.Biomedical engineering, Biomechanicsadb2133Biomedical EngineeringDissertationsApplication of a Novel Quasi-3D Microscopy Technique to Investigate Early Osteocyte Mechanotransduction Eventshttp://academiccommons.columbia.edu/catalog/ac:155780
Baik, Andrew D.http://hdl.handle.net/10022/AC:P:15356Mon, 26 Nov 2012 00:00:00 +0000The objective of this thesis is to observe and characterize the early mechanical and biochemical events in osteocyte mechanotransduction. Physical forces have been increasingly implicated in normal physiological and pathological cellular activities of osteocytes. The mechanotransduction process in osteocytes involves spatiotemporally complex changes in cytoskeletal organization, signal activation, and whole cell mechanical properties. Most in vitro biophysical techniques currently available sacrifice either spatial or temporal resolution and are unable to visualize 3D cellular behavior on the millisecond time scale. Here, we develop a novel multi-channel quasi-3D microscopy technique to simultaneously visualize and measure whole-cell mechanics, intracellular cytoskeletal deformation, and biochemical signal activation under fluid shear flow.The technique was applied to visualize cell dilatation and cytoskeletal deformation in osteocytes under steady fluid shear flow. Analysis of the plasma membrane and either the intracellular actin or microtubule cytoskeletal networks provided characterization of their deformations over time. No volumetric dilatation of the whole cell was observed under flow, and both cytoskeletal networks experienced primarily tensile viscoelastic creep and recovery in all measured strain components. Intra- and inter- cellular mechanical heterogeneity was observed in both cytoskeletal networks. Cytoskeletal disruption pointed towards a unidirectional mechanical interaction where microtubule networks affected actin network strains, but not vice versa.The second study in this thesis investigated the effects of steady and oscillatory flow on the actin and microtubule networks within the same cell. Shear strain was the predominant strain in both steady and oscillatory flows, in the form of viscoelastic creep and elastic oscillations, respectively. Under oscillatory fluid shear flow, the actin networks displayed an oscillatory strain profile more often than the MT networks in all the strains tested and had a higher peak-to-trough magnitude. Taken together with the first study, the actin networks were determined to be the more responsive cytoskeletal networks in osteocytes to fluid flow and may play a bigger role in mechanotransduction.The final culminating study tracked [Ca+2]i and F-actin network strains simultaneously in a single osteocyte. We demonstrated novel osteocyte mechano- and transduction behavior where [Ca+2]i oscillations activate phasic actomyosin contractions using a smooth muscle-like mechanism. Fluid shear, ATP, and ionomycin induced [Ca+2]i signaling with a subsequent compression and recovery in actin strains of the cell, being most apparent in the height direction strain. This contraction was reversible over the period of hundreds of seconds. ML-7, a myosin light chain kinase inhibitor, significantly slowed down the kinetics of contraction initiation, but blebbistatin, a potent skeletal and non-muscle inhibitor, had no effect on the actin contraction. Furthermore, smooth muscle contraction-related proteins were detected by Western blot. The observation of muscle-like contractility in osteocytes demonstrates a possible positive feedback mechanism of osteocytes to activate mechanotransduction pathways.Biomedical engineering, Biomechanicsadb2133Biomedical EngineeringDissertationsSubharmonic Distortion in Ear Canal Pressure and Intracochlear Pressure and Motionhttp://academiccommons.columbia.edu/catalog/ac:148278
Huang, Stanley; Dong, Wei; Olson, Elizabeth S.http://hdl.handle.net/10022/AC:P:13595Fri, 22 Jun 2012 00:00:00 +0000When driven at sound pressure levels greater than ~110 dB stimulus pressure level, the mammalian middle ear is known to produce subharmonic distortion. In this study, we simultaneously measured subharmonics in the ear canal pressure, intracochlear pressure, and basilar membrane or round window membrane velocity, in gerbil. Our primary objective was to quantify the relationship between the subharmonics measured in the ear canal and their intracochlear counterparts. We had two primary findings: (1) The subharmonics emerged suddenly, with a substantial amplitude in the ear canal and the cochlea; (2) at the stimulus level for which subharmonics emerged, the pressure in scala vestibuli/pressure in the ear canal amplitude relationship was similar for the subharmonic and fundamental components. These findings are important for experiments and clinical conditions in which high sound pressure level stimuli are used and could lead to confounding subharmonic stimulation.Audiology, Biomechanicssh2365, wd2015, eao2004Otolaryngology-Head and Neck Surgery, Biomedical EngineeringArticlesAuditory Nerve Excitation via a Non-traveling Wave Mode of Basilar Membrane Motionhttp://academiccommons.columbia.edu/catalog/ac:146628
Huang, Stanley; Olson, Elizabeth S.http://hdl.handle.net/10022/AC:P:13135Fri, 04 May 2012 00:00:00 +0000Basilar membrane (BM) motion and auditory nerve fiber (ANF) tuning are generally very similar, but the ANF had appeared to be unresponsive to a plateau mode of BM motion that occurs at frequencies above an ANFâ€™s characteristic frequency (CF). We recorded ANF responses from the gerbil, concentrating on this supra-CF region. We observed a supra-CF plateau in ANF responses at high stimulus level, indicating that the plateau mode of BM motion can be excitatory.Audiology, Biomechanicssh2365, eao2004Otolaryngology-Head and Neck Surgery, Biomedical EngineeringArticlesMechanical and biochemical properties of human cervical tissuehttp://academiccommons.columbia.edu/catalog/ac:145506
Myers, Kristin M.; Paskaleva, Anastassia; House, Michael; Socrate, Simonahttp://hdl.handle.net/10022/AC:P:12869Thu, 22 Mar 2012 00:00:00 +0000The mechanical integrity of cervical tissue is crucial for maintaining a healthy gestation. Altered tissue biochemistry can cause drastic changes in the mechanical properties of the cervix and contribute to premature cervical dilation and delivery. We present an investigation of the mechanical and biochemical properties of cervical samples from human hysterectomy specimens. Three clinical cases were investigated: nonpregnant hysterectomy patients with previous vaginal deliveries; nonpregnant hysterectomy patients with no previous vaginal deliveries; and pregnant hysterectomy patients at time of cesarean section. Tissue samples were tested in confined compression, unconfined compression and tension. Cervical tissue samples for the three clinical cases were also subjected to biochemical analysis. Biochemical assays measured cervical tissue hydration, collagen content, collagen extractability and sulfated glycosaminoglycan (GAG) content. Results from the mechanical tests indicate that cervical stroma has a nonlinear, time-dependent stress response with varying degrees of conditioning and hysteresis depending on its obstetric background. It was found that the nonpregnant tissue was significantly stiffer than the pregnant tissue in both tension and compression. Further, collagen extractability, sulfated GAG content and hydration were substantially higher in the pregnant tissue. This study is the first important step towards the attainment of an improved understanding of the complex interplay between the molecular structure of cervical tissue and its macroscopic mechanical properties.Biomechanics, Obstetrics and gynecologykmm2233Mechanical EngineeringArticlesThe In Vitro Inflation Response of Mouse Sclerahttp://academiccommons.columbia.edu/catalog/ac:145444
Myers, Kristin M.; Cone, Frances E.; Quigley, Harry A.; Gelman, Scott; Pease, Mary E.; Nguyen, Thao D.http://hdl.handle.net/10022/AC:P:12850Mon, 19 Mar 2012 00:00:00 +0000The purpose of this research was to develop a reliable and repeatable inflation protocol to measure the scleral inflation response of mouse eyes to elevations in intraocular pressure (IOP), comparing the inflation response exhibited by the sclera of younger and older C57BL/6 mice. Whole, enucleated eyes from younger (2 month) and older (11 month) C57BL/6 mice were mounted by the cornea on a custom fixture and inflated according to a load-unload, ramp-hold pressurization regimen via a cannula connected to a saline-filled programmable syringe pump. First, the tissue was submitted to three load-unload cycles from 6 mmHg to 15 mmHg at a rate of 0.25 mmHg/s with ten minutes of recovery between cycles. Next the tissue was submitted to a series of ramp-hold tests to measure the creep behavior at different pressure levels. For each ramp-hold test, the tissue was loaded from 6 mmHg to the set pressure at a rate of 0.25 mmHg/s and held for 30 min, and then the specimens were unloaded to 6 mmHg for 10 min. This sequence was repeated for set pressures of: 10.5, 15, 22.5, 30, 37.5, and 45 mmHg. Scleral displacement was measured using digital image correlation (DIC), and fresh scleral thickness was measured optically for each specimen after testing. For comparison, scleral thickness was measured on untested fresh tissue and epoxy-fixed tissue from age-matched animals. Comparing the apex displacement of the different aged specimens, the sclera of older animals had a statistically significant stiffer response to pressurization than the sclera of younger animals. The stiffness of the pressure-displacement response of the apex measured in the small-strain (6–15 mmHg) and the large-strain (37.5–45 mmHg) regime, respectively, were 287 ± 100 mmHg/mm and 2381 ± 191 mmHg/mm for the older tissue and 193 ± 40 mmHg/mm and 1454 ± 93 mmHg/mm for the younger tissue (Student t-test, p < 0.05). The scleral thickness varied regionally, being thickest in the peripapillary region and thinnest at the equator. Fresh scleral thickness did not differ significantly by age in this group of animals. This study presents a reliable inflation test protocol to measure the mechanical properties of mouse sclera. The inflation methodology was sensitive enough to measure scleral response to changes in IOP elevations between younger and older C57BL/6 mice. Further, the specimen-specific scleral displacement profile and thickness measurements will enable future development of specimen-specific finite element models to analyze the inflation data for material properties.Biomechanics, Ophthalmologykmm2233Mechanical EngineeringArticlesThe Presence and Distribution of Elastin in the Posterior and Retrobulbar Regions of the Mouse Eyehttp://academiccommons.columbia.edu/catalog/ac:145448
Gelman, Scott; Cone, Frances E.; Pease, Mary E.; Nguyen, Thao D.; Myers, Kristin M.; Quigley, Harry A.http://hdl.handle.net/10022/AC:P:12851Mon, 19 Mar 2012 00:00:00 +0000The Presence and distribution of elastin in the posterior and retrobulbar regions of the mouse eye was investigated. Mice of two strains (C57/BL6 and DBA/2J) were studied at 2 months and 8–12 months of age. Light, confocal, and transmission electron microscopy were used to identify elastin, using immunohistochemical techniques and ultrastructural evaluation. Elastin was found in the following ocular structures: conjunctiva, muscle tendons, sclera, choroid, and meninges. The elastin in the sclera was most dense in a ring surrounding the peripapillary optic nerve head, with its presence in the inner sclera declining with greater distance from the nerve head. Elastin fibers were oriented in the sclera along what would be expected to be the principal stress directions generated from the intraocular pressure, though actual biomechanical measurements have not yet been made in the mouse sclera. Elastin comprises a portion of the mouse sclera and its distribution in the peripapillary area is similar to that in human eyes.Biomechanics, Ophthalmologykmm2233Mechanical EngineeringArticlesProtein purification to analyze AAA+ proteolytic machine in vitrohttp://academiccommons.columbia.edu/catalog/ac:143127
Rojas, Diego F.http://hdl.handle.net/10022/AC:P:12138Mon, 09 Jan 2012 00:00:00 +0000The ATP-dependent ClpXP protease of Escherichia coli consists of two subunits, the ClpP subunit, which has the proteolytic activity and the AAA+ motor ClpX, which mechanically unfolds and translocates substrates for ClpP degradation. In order to investigate the mechanical properties of ClpXP during substrate unfolding using magnetical tweezers, here we optimize protocols to purify ClpP and a model substrate based on human Filamin A from E. coli lysates by a combination of metal affinity chromatography and fast performance liquid chromatography (FPLC). ClpX purification was challenging and remains to be improved. Importantly, a HaloTag protein molecule was fused to the Filamin substrate, which allowed covalent bonding to surfaces or fluorescent molecules. We analyzed the mechanical properties of a single Filamin A substrate using atomic force spectroscopy (AFM) and found good correlation with previous single-molecule experiments based on optical tweezers. AFM experiments also demonstrate the successful binding of the HaloTag moiety to a modified glass surface. The results show that the study of ClpXP-mediated degradation of proteins by magnetic tweezers has the potential to unveil the mechanics of protein degradation inside cells.Biomechanicsdfr2111Biological SciencesArticlesThe inflation response of the posterior bovine sclerahttp://academiccommons.columbia.edu/catalog/ac:143121
Myers, Kristin M.; Coudrillier, Baptiste; Boyce, Brad L.; Nguyen, Thao D.http://hdl.handle.net/10022/AC:P:12134Mon, 09 Jan 2012 00:00:00 +0000An in vitro inflation test method was developed to characterize the mechanical behavior of the bovine posterior sclera. The method used digital image correlation to provide a spatially resolved, full-field deformation map of the surface of the posterior sclera in response to controlled pressurization. A series of experiments were performed in the range of 2-6 kPa (15-45 mmHg) to characterize the load-unload displacement response at various pressure rates and the time-dependent displacement response at different applied pressures. The magnitude of the displacement was largest in the peripapillary region, mainly between the apex and the optic nerve head. Further, the results showed that bovine scleral tissue exhibited nonlinear and viscoelastic behavior characterized by a rate-dependent displacement response, hysteresis during unloading and creep. The creep rate was insensitive to the applied pressure, suggesting that the tissue can be modeled as a quasilinear viscoelastic material in the physiological pressure range of 2-6 kPa.Materials science, Biomechanicskmm2233Mechanical EngineeringArticlesSubharmonics and Auditory Nerve Tuning Curves in Gerbilhttp://academiccommons.columbia.edu/catalog/ac:143097
Huang, Stanley; Dong, Wei; Olson, Elizabeth S.http://hdl.handle.net/10022/AC:P:12133Mon, 09 Jan 2012 00:00:00 +0000In the literature, an auditory nerve tuning curve obtained from single unit recording typically has a tail and a tip. Responses beyond the tip in the well supra-CF frequency region had never been documented. In a study designed to explore that region specifically, we found plateau responses in the supra-CF region of several auditory nerve tuning curves at very high sound pressure levels (~120dB SPL). (Huang & Olson, ARO 2009, poster #623) However, a complicating issue at high sound pressure levels is the generation of subharmonics, which are likely generated in the eardrum (Dallos & Linnell 1966 JASA 40(3):561-564). Indeed, we found subharmonics in a subset of ear canal pressure we measured in gerbils, and they might have contributed to the supra-CF responses. Here we present auditory nerve tuning curves in which supra-CF neural responses were present while subharmonics were beneath the noise floor in the ear canal pressure. Thus these detections of supra-CF neural responses did not seem to suffer from subharmonic "contamination." To probe this further, we delivered loud tones and compared ear canal pressure and intracochlear pressure at subharmonics frequencies, and the quantitative relationship between the two reinforced that subharmonics were probably not responsible for the supra-CF neural responses we measured. It is conceivable that this subharmonic finding has at least two clinical implications. First, eardrum produced subharmonics might occur with very high power hearing aids. This could pose a problem to patients with band limited or high frequency hearing loss, since subharmonics that are within their normal-hearing frequencies could be perceived to be "louder" than the fundamental. Second, we found that the eardrum (the putative source of the subharmonics) was a reasonably effective sound radiator. Thus hearing aids that drive the eardrum directly might produce feedback.Biomechanics, Biomedical engineering, Health sciencessh2365, wd2015, eao2004Otolaryngology-Head and Neck Surgery, Biomedical EngineeringPresentationsHigh Frequency Plateau in Gerbil Auditory Nerve Tuning Curveshttp://academiccommons.columbia.edu/catalog/ac:143094
Huang, Stanley; Olson, Elizabeth S.http://hdl.handle.net/10022/AC:P:12132Mon, 09 Jan 2012 00:00:00 +0000Ruggero et al. (PNAS 97(22) p.11744, 2000) compared threshold tuning curves of chinchilla basilar membrane (BM) vibrations and auditory nerve (AN) fibers. They noted that the AN tuning curves lacked the supra-CF frequency plateaus that are present in BM responses and suggested that BM vibrations do not translate into AN responses in the supra-CF frequency region. This observation is relevant to the relationship between BM motion (macromechanics) and hair cell stimulation (micromechanics). To further investigate the discrepancy, we recorded AN responses from the gerbil, concentrating on the supra-CF region of single AN fibers. We observed a supra-CF frequency plateau in AN responses at very high sound pressure levels (> 100dB SPL). This AN plateau was at least 10 to 15dB higher than what is predicted from BM plateaus. However, at high sound pressure levels, we also recorded subharmonics in the acoustic signal in the ear canal. The subharmonics were not produced by the speaker and appeared to be produced in the auditory mechanics. Dallos and Linnell (JASA 40(3) p.561, 1966) studied similar subharmonics, and concluded that they were produced in the ear drum and in the cochlea. We still need to determine whether the subharmonics are responsible for the supra-CF frequency plateaus in the AN responses or if the AN responses are due to the motion of the BM at the fundamental frequency.Biomechanics, Biomedical engineering, Health sciencessh2365, eao2004Otolaryngology-Head and Neck Surgery, Biomedical EngineeringPresentationsSupra-Characteristic-Frequency Response in Gerbil Auditory Nerve Frequency Tuning Curveshttp://academiccommons.columbia.edu/catalog/ac:139281
Huang, Stanleyhttp://hdl.handle.net/10022/AC:P:11292Wed, 28 Sep 2011 00:00:00 +0000Sound arriving at the ear causes the vibration of the sensory tissues, including the basilar membrane (BM), inside the cochlea and, in turn, leads to inner hair cell excitation and auditory nerve fiber (ANF) responses. The goal of this study is to better understand the mechanics of inner hair cell excitation which leads to hearing. BM motion and ANF tuning are generally very similar, but the ANF had appeared to be unresponsive to a plateau mode of BM motion that occurs at frequencies above an ANF's characteristic frequency (CF). We recorded ANF responses from the gerbil, concentrating on this supra-CF region. We observed a supra-CF plateau in ANF responses at high stimulus level, indicating that the plateau mode of BM motion can be excitatory. Quantitative aspects of our findings suggest that the differential longitudinal motion that occurs within the traveling wave but not the plateau mode increases the sensitivity of inner hair cell excitation. The main findings of this study include: The detection of the plateau threshold within the supra-CF region of the ANF tuning curve. A larger BM motion was necessary for an ANF to reach a threshold response within the plateau region than the traveling wave region, based on the previous lack of ANF plateau threshold detection and a comparison to the BM plateau levels in the literature. Stimuli used in this study, even though unnaturally high in level, advanced our understanding of cochlear mechanics. However, at high sound pressure levels used, the middle ear generated subharmonic distortions that could produce confounding effects in the plateau responses. Hence, we also characterized the subharmonics and were able to rule out the possibility that they were solely responsible for the plateau responses we observed.Biomechanics, Biomedical engineering, Health sciencessh2365Otolaryngology-Head and Neck Surgery, Biomedical EngineeringDissertations